1. Field of the Invention
This invention relates to a device for retracting and winding up automatically a seat belt used in a vehicle to protect the occupant, and more particularly to a mechanism for controlling the force for retracting or winding up the seat belt.
2. Description of the Related Art
There have conventionally been known seat belt retracting and winding devices which contain a winding reel and spring means having one end connected to the winding reel and the other end connected to a frame of the device. This spring means is constituted by two spiral springs connected to each other through an interposed ratchet means. These devices control the combined spring force of the two springs in dependence on whether a pawl is engaged with the ratchet means or not, thereby exerting a reduced retracting and winding force to the seat belt after it has been fastened across the vehicle occupant.
Devices of this type are known from U.S. Pat. No. 4,382,563 entitled "Seat Belt Winding and Retracting Apparatus" and from U.S. Pat. No. 4,383,658, entitled "Seat Belt Retracting and Winding Devie". According to the former patent, electromagnetic means selectively actuates the pawl so that the starting condition which a reduced retracting and winding force is exerted to the seat belt, may adjust in dependence on the states of the vehicle or physique of the occupant, while the occupant needs to manually operate a switch for energizing the electromagnetic actuator means and the reliability in operation is inferior to the latter patent. A disadvantage of the latter patent is that means for controlling the pawl is complex and difficult to be manufactured. A further disadvantage of the latter patent is that the starting condition which a reduced retracting and winding force is exerted to the seat belt, is hardly adjustable in dependence on the states of the vehicle or physique of the occupant.